The invention pertains to rigid magnetic disk drives and more particularly to a method of controlling the idling location of the transducer supporting sliders over the disk surface in response to the migration disk surface lubricant over time to extend the useful life of the drive.
When rigid magnetic disks are manufactured, a typical lubricant is applied to protect the data surface from damage arising from occasional, accidental contact with the transducer head that flies over the surface during disk drive operation. The lubricant is normally a type that forms a chemical bond with the underlying disk surface coating. However such bonding is limited to a thin layer at the interface surface, with the result that a thin film of lubricant is bonded and stationary while the remainder is mobile and subject to migration when subjected to centrifugal forces as the disk rotates at high rotational velocities or head pressure as the head flies over and is supported above the surface by a film of air.
Centrifugal forces cause the lube to migrate toward the outer edges of the disks leaving the inner radii with less lube and therefore more susceptible to wear during intermittent slider-to-disk contact. If sliders are allowed to idle near the inner tracks after the lube has migrated from that vicinity, the result will be more frequent slider-disk contact that will accelerate failure.
This invention recognizes the occurrence of lubricant migration toward the perimeter of the disk as a result of high rotational speed disk rotation. If sliders are allowed to idle near the inner diameter tracks after lube has migrated from that location, failure will be accelerated. After a power on operational time period, during which experience has shown that significant lube migration has taken place, the sliders are moved during idle time toward the outer (larger radius) tracks to reduce the amount of time the sliders spend over the low lube regions at smaller radii on the disk surfaces. Initially, the lube thickness is substantially identical over the entire disk data surface. However, it has been found that after a period of about three months of continuous operation (spinning of the disks) much of the mobile portion of the lube has migrated toward the outer radius of the disk surface, leaving the inner radius tracks with little but the bonded lubricant remaining.
One response to the problem is to change the track distribution for idle to follow the lube migration over time. At low power on hours, the track distribution is broad and covers the entire disk surface. This is important because it prevents any area of the disk from becoming a collection area for debris. If, for example, an inner radii region of the disks were completely neglected during idle, a ridge of debris may develop at the edge of the idle zone. An analogy is the debris that accumulates at the edge of highways where vehicles seldom pass over. If a car, for example, moves onto the shoulder of a highway, it is likely that some debris will be hit. In the same way, if debris collects at the edge of an idle zone, it can cause a head crash when struck for the first time. Therefore, it is necessary to periodically sweep the entire disk data surface from inner diameter to outer diameter even after much of the lube has migrated to the outer disk radii and the idle function has been modified to position the sliders only over disk surface portions that are most adequately lubricated.
Thus, although the sliders are controlled to idle over a band of tracks at the outer diameter of the disk data surfaces to match the lube migration, the sliders are periodically moved to the innermost track and then moved to the outer diameter track in order to sweep the entire disk surface and eliminate debris.